Elastomer composition comprising polyolefin elastomers

ABSTRACT

Disclosed is an elastomer composition comprising polyolefin elastomer material which exhibits improved hysteresis properties, said elastomer composition having the following properties:
     (1) an average integrated enthalpy sum of no greater than 17 J/g according to the Thermal Analysis Method defined herein;   (2) an average integrated enthalpy ratio of from 0.6 to 300 according to the Thermal Analysis Method defined herein;   (3) an unload stress at 75% strain of above 0.8 MPa according to the Hysteresis Test defined herein; and   (4) a load stress/unload stress ratio at 75% strain of 1 to 2.6 according to the Hysteresis Test defined herein.

FIELD OF THE INVENTION

The present invention relates to an elastomer composition comprisingpolyolefin elastomer which exhibits improved hysteresis properties.

BACKGROUND OF THE INVENTION

Elastic materials, especially elastic films, are commonly used for awide variety of applications. For example, absorbent articles typicallyinclude one or more components that rely on film materials, especiallyelastic film materials, to control the movement of liquids and toprovide a comfortable, conforming fit when the article is worn by awearer. A typical way of introducing elastic material in an absorbentarticle is either though waistbands, leg elastics, side panels, elasticbelts, stretch outer cover or stretch ears. Hysteresis behavior, i.e.the load to unload performance in tensile testing, is a good measure ofhow well the product performs and it is often associated with theelastic materials used in the article.

Conventional elastic film materials made out of styrenic blockcopolymers and/or polyurethanes may provide favorable hysteresisperformance, but may also undesirably impact the cost and/or complexityof manufacturing the product. With recent metallocene chemistrydevelopment, a new class of elastic polyolefins including, but notlimited to random copolymerized propylene with ethylene, have becomeavailable for product application, such as described in US PatentApplication publication US 2005/0171285A and PCT Patent Publication WO2007/053603. While these materials deliver certain hysteresisperformance, there is yet room for improvement, without significant costadded for making the material.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a systematic representation of the measurement methods for theInitial Tensile Test and the Hysteresis Test defined herein.

FIG. 2(a)-(d) are systematic representations of the data correctionmethod for the Thermal Analysis Method defined herein.

FIG. 3(a)-(b) describe an embodiment of the base line corrected DSCchart according to the Thermal Analysis Method defined herein of anelastomer composition of the present invention.

FIG. 4(a)-(h) are the base line corrected DSC charts according to theThermal Analysis Method defined herein of Examples 1 to 8.

SUMMARY OF THE INVENTION

In order to provide a solution to the opportunity for improvement setforth above, an elastomer composition which comprises polyolefinelastomers is disclosed. The composition exhibits suitable hysteresisproperties as well as acceptable robustness to tensile stress withoutsignificant cost added for making the material.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

“Absorbent article” means a device that absorbs and contains bodyexudates and, more specifically, devices that are placed against or inproximity to the body of the wearer to absorb and contain the variousexudates discharged from the body. Exemplary absorbent articles includediapers, training pants, pull-on pant-type diapers (i.e., a diaperhaving a pre-formed waist opening and leg openings such as illustratedin U.S. Pat. No. 6,120,487), refastenable diapers or pant-type diapers,incontinence briefs and undergarments, diaper holders and liners,feminine hygiene garments such as panty liners, absorbent inserts, andthe like.

“Activation” is the mechanical deformation of a plastically extensiblematerial that results in permanent elongation of the material in thedirection of activation. Activation of a laminate that includes anelastic material joined to a plastically extensible material typicallyresults in permanent deformation of the plastically extensible material,while the elastic material returns substantially to its originaldimension. “Activate”, and variations thereof, means subjecting amaterial to an activation process.

“Aperture” means an opening in a film purposefully added during filmmaking or laminate making, which is intended to impart a desiredcharacteristic such as breathability. “Basis weight” is the property ofa sheet or web of material calculated as the mass of the materialdivided by its surface area. The units for basis weight herein are gramsper square meter (g/m²).

“Breathable” means a film or laminate that has an Air Permeability Valueof between 5.0 and 50 m³/m²/min according to the Air Permeability Testdescribed below.

“Copolymer” means a polymer derived from two or more monomer specieswherein the polymer chains each comprise repeat units from more than onemonomer species.

“Crystalline melting temperatures” are determined by DifferentialScanning calorimetry, for example, as described below in the ThermalAnalysis method. Materials may have one or more melting endotherm peaks.

“Disposed” means an element is positioned in a particular place withregard to another element.

“Extensible” means the ability to stretch or elongate, without ruptureor breakage, to at least 130% strain, for example, as described below inthe Hysteresis Test.

“Elastic,” “elastomeric,” and “elastically extensible” mean the abilityof a material to stretch by at least 130% strain without rupture orbreakage at a given load, and upon release of the load the elasticmaterial or component exhibits at least 70% recovery (i.e., has lessthan 30% set). For example, an elastic material that has an initiallength of 25.4 mm can stretch to at least 58.4 mm (130% stretch) and,upon removal of the force, retract to a length of 30.5 mm (i.e., have aset of 5.1 mm or 20%). Stretch, sometimes referred to as strain, percentstrain, engineering strain, draw ratio, or elongation, along withrecovery and set may each be determined according to the Hysteresis Testdescribed below. Materials that are extensible but not “elastic” areconsidered “plastically extensible” materials.

“Film” means a sheet-like material wherein the length and width of thematerial far exceed the thickness of the material (e.g., 10 times, 50times, or even 1000 times or more). Films are typically liquidimpermeable but may be configured to be breathable.

“Joined” means configurations whereby an element is directly secured toanother element by affixing the element directly to the other element,and configurations whereby an element is indirectly secured to anotherelement by affixing the element to intermediate member(s) that in turnare affixed to the other element.

“Laminate” means two or more materials that are bonded to one another byany suitable method known in the art (e.g., adhesive bonding, thermalbonding, ultrasonic bonding, or high pressure bonding using non-heatedor heated patterned roll).

“Longitudinal” means a direction running substantially perpendicularfrom a waist end edge to an opposing waist end edge of an absorbentarticle when the article is in a flat out, uncontracted state, or from awaist end edge to the bottom of the crotch in a bifolded article.Directions within 45 degrees of the longitudinal direction areconsidered to be “longitudinal.” “Lateral” refers to a direction runningfrom a side edge to an opposing side edge of an article and generallyperpendicular to the longitudinal direction. Directions within 45degrees of the lateral direction are considered lateral.

“Machine direction” or “MD” is the direction parallel to the directionof travel of the film in which it is extruded or the web in amanufacturing process. Directions within 45 degrees of the MD areconsidered to be machine directional. The “cross machine direction” or“CD” is the direction substantially perpendicular to the MD and in theplane generally defined by the film or web. Directions within 45 degreesof the CD are considered to be cross directional.

“Nonwoven” means a porous, fibrous material made from continuous (long)filaments (fibers) and/or discontinuous (short) filaments (fibers) byprocesses such as, for example, spunbonding, meltblowing, airlaying,carding, coforming, hydroentangling, and the like. Nonwovens do not havea woven or knitted filament pattern. Nonwovens may be liquid permeableor impermeable.

“Relaxed” means the state of an element, material or component at restwith substantially no external force acting on the element, other thangravity.

“Web” means a material capable of being wound into a roll. Webs may befilms, nonwovens, laminates, apertured films and/or laminates, and thelike. The face of a web refers to one of its two dimensional surfaces,as opposed to its edge.

“X-Y plane” means the plane defined by the MD and CD of a moving web orthe length and width of a piece of material.

Elastomer Composition

Semi-crystalline, or metallocene polyolefins are widely used indisposable absorbent products. It is known that their performancedepends on amount of crystallinity. The crystallinity decreases withdecreasing stereo-regularity, and the material shows more elasticbehavior. A number of methods are known for controlling crystallinity,such as by introducing stereo-irregularity or by introducing acomonomer. Some homopolyolefins and random copolymers, as well as blendsof such random copolymers, known by tradenames Vistamaxx™ available fromExxonMobil and VERSIFY™ from Dow Corning, are synthesized based on thisprinciple, and tend to show elastic performance. While these materialsdeliver certain hysteresis performance, there is yet room forimprovement, without significant cost added for making the material.

The elastomer composition of the present invention may be made bymodifying or blending one or more polyolefin elastomer materials thathave elastic properties, according to the definition herein. Thepolyolefin elastomer materials useful herein include, but are notlimited to, any polymers or copolymers of polyolefins such aspolyethylene and polypropylene. Particularly suitable examples ofelastic materials include elastomeric polypropylenes. In thesematerials, propylene represents the majority component of the polymericbackbone, and as a result, any residual crystallinity possesses thecharacteristics of polypropylene crystals. Residual crystalline entitiesembedded in the propylene-based elastomeric molecular network mayfunction as physical crosslinks, providing polymeric chain anchoringcapabilities that improve the mechanical properties of the elasticnetwork, such as high recovery, low set and low force relaxation.Suitable examples of elastomeric polypropylenes include an elasticrandom poly(propylene/olefin) copolymer, an isotactic polypropylenecontaining stereo-irregularity, an isotactic/atactic polypropylene blockcopolymer, an isotactic polypropylene/random poly(propylene/olefin)copolymer block copolymer, a stereoblock elastomeric polypropylene, asyndiotactic polypropylene block poly(ethylene-co-propylene) blocksyndiotactic polypropylene triblock copolymer, an isotacticpolypropylene block regio-irregular polypropylene block isotacticpolypropylene triblock copolymer, a polyethylene random(ethylene/olefin) copolymer block copolymer, a reactor blendpolypropylene, a very low density polypropylene (or, equivalently, ultralow density polypropylene), a metallocene polypropylene, and blends orcombinations thereof. Suitable polypropylene polymers includingcrystalline isotactic blocks and amorphous atactic blocks are described,for example, in U.S. Pat. Nos. 6,559,262, 6,518,378, and 6,169,151.Suitable isotactic polypropylene with stereo-irregularity along thepolymer chain are described in U.S. Pat. No. 6,555,643 and EP 1 256 594A1. Suitable examples include elastomeric random copolymers includingpropylene with a low level comonomer (e.g., ethylene or a higheralpha-olefin) incorporated into the backbone.

The elastomer composition of the present invention may be made byblending at least two (2) polyolefin elastomer materials. The polyolefinelastomer materials useful for preparing the present elastomercomposition in such manner include metallocene polypropylene, and thosehaving a crystalline melting point of at least 75° C., or at least 80°C., as defined by the Thermal Analysis Method defined herein. Suchpolyolefin elastomer materials may be selected from commerciallyavailable material such as, but not limited to: Vistamaxx 6102(available from ExxonMobil, Houston, Tex.), random propylene-ethylenecopolymers; NOTIO PN-0040 and PN-2070 (available from Mitsui Chemicals,Tokyo Japan), elastic polyolefin resins; L-MODU X901S (available fromMitsui Chemicals, Tokyo Japan): a stereo copolymer of polypropylene;Versify 2400A, 2400B, 3401A and 3401 B (available from Dow Chemical,Midland, Mich.), random copolymers of propylene with ethylene.

The elastomer composition of the present invention may include one ormore additives commonly used in the art to tailor the composition for aparticular use. For example, stabilizers, antioxidants, andbacteriostats may be employed to prevent thermal, oxidative, andbio-chemical degradation of the elastomer composition. Generally, theadditive or additives may account for 0.01% to 20%; 0.01% to 10%; or0.01% to 2% of the total weight of the elastomer composition.

Suitable examples of stabilizers and antioxidants include high molecularweight hindered phenols (i.e., phenolic compounds with sterically bulkyradicals in proximity to the hydroxyl group), multifunctional phenols(i.e., phenolic compounds with sulfur and phosphorous containinggroups), phosphates such as tris-(p-nonylphenyl)-phosphite, hinderedamines, and combinations thereof. Representative hindered phenolsinclude t-butylhydroxyquinone;1,3,5-trimethyl-2,4,6-tris(3-5-di-tert-butyl-4-hydroxybenzyl) benzene;pentaerythritol tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;n-octadecyl-3(3,5-ditert-butyl-4-hydroxyphenyl)propionate;4,4′-methylenebis(4-methyl-6-tert butylphenol);4,4′-thiobis(6-tert-butyl-o-cresol); 2,6-di-tert-butylphenol;6-(4-hydroxyphenoxy)-2,4-bis(n-ocytlthio)-1,3,5-triazine;2,4,6-tris(4-hydroxy-3,5-di-tert-butyl-phenoxy)-1,3,5-triazine;di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate;2-(n-octylthio)ethyl-3,5-di-tert-butyl-4-hydroxybenzoate; and sorbitolhexa-(3,3,5-di-tert-butyl-4-hydroxy-phenyl)propionate. Proprietarycommercial stabilizers and/or antioxidants are available under a numberof tradenames including a variety of Wingstay®, Tinuvin® and Irganox®products.

Examples of suitable bacteriostats include benzoates, phenols,aldehydes, halogen containing compounds, nitrogen compounds, andmetal-containing compounds such as mercurials, zinc compounds and tincompounds. A representative bacteriostat is2,4,4′-trichloro-2′-hydroxy-diphenyl-ether which is available under thetrade designation IRGASAN PA from Ciba Specialty Chemical Corporation,Tarrytown, N.Y.

Various viscosity modifiers, processing aids, slip agents or anti-blockagents can be employed as additives to provide improved handlingcharacteristics or surface characteristics. Processing aids includeprocessing oils, which are well known in the art and include syntheticand natural oils, naphthenic oils, paraffinic oils, olefin oligomers andlow molecular weight polymers, vegetable oils, animal oils, andderivatives of such including hydrogenated versions. Processing oilsalso may incorporate combinations of such oils. A particularly suitableprocessing oil is mineral oil.

A variety of fillers can also be used as additives to the elastomercomposition. Examples of suitable fillers include talc, calciumcarbonate, carbon black, clay, and mica. The filler may be selected incombination with antioxidants to minimize impact on stability.

A wide range of pigments can also be employed to impart desirable colorto the elastomer composition. Organic and inorganic pigments such asazo, quinacridone, cadmium, and chrome containing pigments may beblended with the elastomer composition.

Nucleating agents such as sorbitol based compounds, sodium salts oforganic phosphates, sodium benzoate may be used in combination with theelastomer composition. They help improve optical properties and physicalproperties of the elastomer composition.

Compatiblizers can also be used in combination with the elastomercomposition. They help improve interfacial adhesion between components.This often results in better mechanical and/or optical properties.

The elastomer composition of the present invention may be used inextrusion processes to produce products, such as fiber or film forms.Fibers may be meltblown and/or spun to form nonwovens. The elastomercomposition can be cast or blown to make a sheet. The elastomercomposition may be used in combination with other resins, either blendedor as separate layers to form fibers or sheets. The elastomercomposition of the present invention may also be blow molded orinjection molded using techniques available in the industry.

The elastomer composition of the present invention may be formed by anysuitable method in the art, for example, by extruding moltenthermoplastic and/or elastomeric polymers through a slit die andsubsequently cooling the extruded sheet. Other non-limiting examples formaking film forms include casting, blowing, solution casting,calendering, and formation from aqueous or, non-aqueous castdispersions. One suitable method for obtaining the elastomer compositionof the present invention in the film form is by allowing polyolefinelastomers or other materials obtained in pellet form to be mixed andextruded by a high torque co-rotating twin-screw extruder, namelyextrusion blending. The elastomer composition of the present inventionmay be made into a film having a basis weight of from about 5 to about150 g/m², preferably from about 10 to about 100 g/m².

The elastomer composition of the present invention preferably has acrystalline melting point of at least 75° C., or at least 80° C., asdefined by the Thermal Analysis Method defined herein. Without beingbound by theory, it is believed that the elastomer composition of thepresent invention having such melting point may provide betterhysteresis, and further provide better stability at relatively hightemperature storage conditions.

According to the Hysteresis Test defined herein, the elastomercomposition of the present invention exhibits an unload stress at 75%strain of greater than 0.80 MPa. According to the Hysteresis Test, theelastomer composition of the present invention exhibits a loadstress/unload stress ratio at 75% strain of between 1.0 and 2.6. Theelastic film of the present invention show desired hysteresis propertiesat a low basis weight after straining, which is a treatment typicallyundergone for an elastic element used on a product. Without being boundby theory, it is believed that such properties provide good fit requiredof, for example, absorbent articles.

According to the Thermal Analysis Method, the elastomer composition ofthe present invention exhibits characteristic crystalline meltingproperties when the regions are divided into 3 temperature zones: Zone Ibetween 30-80° C., Zone II between 80-120° C., and Zone III between120-170° C. Without being bound by theory, it is believed that Zones Iand III provide a correlation between crystallinity and hysteresisperformance. The elastomer composition of the present invention exhibitsan average integrated enthalpy sum of Zones I and III of no greater than17 J/g, preferably between about 5-17 J/g. Further, the elastomercomposition of the present invention has an average integrated enthalpyratio of Zone I to Zone III of from 0.6 to 300, preferably 0.8 to 300 orstill preferably 1.0 to 300.

According to the Initial Tensile test, the elastomer composition of thepresent invention exhibits a stress at break value of greater than 10MPa and/or a % strain at break of greater than 500%. By having such highstress at break and/or % strain at break, the elastic film comprisingthe composition is believed to be tough enough for activation, andexhibit appropriate endurance during processing for making an elasticmaterial, or assembling an article using such elastic film.

The elastic film of the present invention shows desired performance as amono-layer film, and may be co-extruded with other materials to form amulti-layer film. One or more layers of the multi-layer film can be askin layer, which helps prevent blocking. The skin layer is preferablymade of plastically extensible materials. A layer in the multi-layerfilm can be provided as a tie layer, which provides good boundarystrength with two non-bondable adjacent layers. The elastic film of thepresent invention may further be apertured to impart breathability.

The elastic film of the present invention having a basis weight of fromabout 5 to about 150 g/m² may be laminated with other plastic films,nonwovens, and/or substrates. Such laminates are useful as elasticelements for absorbent articles such as diapers, feminine pads, bibs,linens, pet sheets, wound dressings, hospital gowns, and the like.Elements useful for making with the laminates include, but are notlimited to, waistbands, leg elastic, side panels, elastic belts, stretchouter cover or stretch ears.

Test Methods

1. Basis Weight, Initial Tensile Test, and Hysteresis Test

1-1. Sample Preparation

If necessary, the product part comprising the elastomer composition(e.g. stretch ear) is cut from the product. If the elastomer compositionis bonded or attached to other components, then it is separated from theother components such as laminated nonwoven layers by techniques such asapplying “Quik-Freeze®” type cold spray, or other suitable methods thatdo not permanently alter the properties of the elastomer composition.Care should be taken to prevent stretching of the elastomer compositionduring the separation process. If the elastomer composition isstandalone, it is used as is for further sample preparation. The sampleis in the form of a film having a basis weight of between 5 and 150g/m². If the sample has a greater basis weight than such range, thesample is sliced into an appropriate basis weight.

The direction in which the elastic film will stretch in its intended useis considered the primary stretch direction of the material. Forstandalone films, where the primary stretch direction is not known, thedirection in which the film has greatest extensibility is assumed to bethe primary stretch direction. Two sets (Set A and Set B) of specimensare cut. A first set (Set A) of rectilinear specimens at least 30 mmlong in the primary stretch direction, and 25.4 mm wide in theperpendicular direction, is cut from the center portion of the productpart. Similarly, a second set (Set B) of rectilinear specimens with 25.4mm width in primary direction and 30 mm length in the perpendiculardirection, is cut from the center portion of the identical product part.Articles having areas of film smaller than 30×25.4 mm are considered tobe outside the scope of this method. Five specimens are cut from thesame portion of identical products for each set. The basis weight ofeach film specimen is measured. If the difference in the elastic filmspecimen basis weight is more than 10% between highest and lowest basisweight samples for any set, then specimens are re-collected for that setfrom a different part of the film, or from fresh products. Each set isanalyzed by the methods described below. For the Initial Tensile Testand Hysteresis Test, the direction in which specimen has longerdimension is considered the specimen direction of stretching.

1-2. Specimen Weight and Basis Weight

Each specimen is weighed to within ±0.1 milligram using a digitalbalance. Specimen length and width are measured using digital Verniercalipers or equivalent to within ±0.1 mm. All testing is conducted at22±2° C. and 50±10% relative humidity. Basis weight is calculated usingequation below.

${{Basis}\mspace{14mu}{{Weight}\left( \frac{g}{m^{2}} \right)}} = \frac{\left( {{Weight}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{specimen}\mspace{14mu}{in}\mspace{14mu}{grams}} \right)}{\begin{matrix}\left( {{Length}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{specimen}\mspace{14mu}{in}\mspace{14mu}{meter}} \right) \\\left( {{Width}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{specimen}\mspace{20mu}{in}\mspace{14mu}{meter}} \right)\end{matrix}}$1-3. Tensile Test Setup

A suitable tensile tester interfaced with a computer such as MTS modelAlliance RT/1 with TestWorks 4® software or equivalent is used. Thetensile tester is located in a temperature-controlled room at 22° C.±2°C. and 50±10% relative humidity. The instrument is calibrated accordingto the manufacturer's instructions. The data acquisition rate is set toat least 50 Hertz. The grips used for the test are wider than thesample. Grips having 50.8 mm width may be used. The grips are airactuated grips designed to concentrate the entire gripping force along asingle line perpendicular to the direction of testing stress having oneflat surface and an opposing face from which protrudes a half round(radius=6 mm, e.g. part number: 56-163-827 from MTS Systems Corp.) orequivalent grips, to minimize slippage of the specimen. The load cell isselected so that the forces measured are between 10% and 90% of thecapacity of the load cell used. The initial distance between the linesof gripping force (gauge length) is set at 25.4 mm. The load reading onthe instrument is zeroed to account for the mass of the fixture andgrips.

The specimen is mounted into the grips in a manner such that there is noslack and the load measured is between 0.00 N and 0.02 N. The specimenis mounted in the center of the grips, such that the specimen directionof stretching is parallel to the applied tensile stress.

1-4. Initial Tensile Test

The instrument is set up and the specimen mounted as described in theTensile Test Setup above. The tensile test is initiated and the specimenis extended at 254 mm/min, with a data acquisition rate of at least 50Hertz, until the specimen breaks, typically 800-1000% strain. The %Strain is calculated from the length between grip lines L, and initialgauge length, L₀, as illustrated in FIG. 1, using the following formula:

${\%\mspace{14mu}{Strain}} = {\frac{\left( {L - L_{0}} \right)}{L_{0}} \times 100}$

Five specimens of each set are measured, and the arithmetic average offorce at 130% strain (N), force at break (N), stress at 130% strain(MPa), stress at break (also called Tensile Strength, MPa), and % Strainat break are recorded. % Strain at break is defined as the % Strain atpeak force. Data are generated for Set A and Set B.Stress in MPa is calculated as follows: Stress=[measuredforce]/[specimen cross-sectional area].

Specimen cross-sectional area is calculated from specimen weight, W (g);before straining specimen length, 1 (mm); and density of the material, ρ(g/cm³). Specimen cross-sectional area A₀ (mm²) is given by formula:A₀=[W×10³]/[ρ×l].

A density of 0.862 grams/cm³ is used for all specimens.

1-5. Hysteresis Test

The instrument is set up and the specimen is mounted as described in theTensile Test Setup section above. Data acquisition rate is set to atleast 50 Hertz.

The Hysteresis Test method for film specimens involves the followingsteps (all strains are strains):

-   (1) Strain the specimen to 130% strain at a constant crosshead speed    of 25.4 cm per minute.-   (2) Hold specimen at 130% strain for 30 seconds.-   (3) Go to 0% strain at a constant crosshead speed of 25.4 cm per    minute.-   (4) Hold specimen for 1 minute at 0% strain.-   (5) Pull the specimen to 0.127 N force and return to 0% strain with    no hold time.    The measured and recorded forces, in Newtons (N), are the load force    at 75% strain in step (1) and the unload force at 75% strain in step    (3). Specimen length at 0.127 N force in step (5) is also recorded    and used to calculate the % set in the material as below.    % Set=((Length at 0.127 N force−Original Gauge length)/Original    Gauge length))×100

The forces are normalized to stress in MPa as follows: Stress=[measuredforce at given strain, in Newtons]/[Cross-sectional area, in mm²].

Specimen cross-sectional area is calculated as described above in theInitial Tensile method.

Unload stress at 75% strain is reported in MPa, and ratio of loadstress/unload stress at 75% strain is reported.

Five specimens of each film set are measured, and the arithmetic averageis calculated for each of the recorded hysteresis parameters for set Aand Set B. The set with the lower load stress/unload stress ratio isused for determination of all claimed parameters, including % Strain atbreak, stress at break, and hysteresis unload stress.

2. Thermal Analysis Method

Approximately 3 milligrams of film are enclosed into a DSC (differentialscanning calorimetry) pan. The weight of the specimen is recorded towithin ±0.1 mg and used for any calculation performed using theinformation collected from DSC run.

The thermal properties of the specimen are measured by DSC using a DSCQ2000 V23.10 Build 79 from Perkin Elmer, or equivalent instrument. Thespecimens are analyzed using standard procedures such as outlined inASTM D3418-08. This method is capable of determining the temperatureranges over which phase changes occur, e.g., glass transition orcrystalline melting. The procedure is modified as follows to carry outtwo heating cycles.

1: Equilibrate at −90.00° C. for 5 min

2: Ramp up at 20.00° C./min to 200.00° C.

3: Isothermal for 5.00 min

4: Ramp down at 20.00° C./min to −90.00° C.

5: Isothermal for 5.00 min

6: Ramp up at 20.00° C./min to 200.00° C.

The heat flow data collected are used for analyzing crystallinity of thematerial. The first heat curve (step 2 above) data are used for thecalculation of heat of fusion using the method described below.

In order to determine accurate heat flow, a mathematical baselinesubtraction is performed using 3^(rd) order polynomial baseline fit.First the raw data from DSC, heat flow in W/g versus temperature (° C.),is obtained in Microsoft Excel format. The data are then curtailed to auseful temperature range of −10° C. to 200° C., and Heat Flow (W/g) isplotted as a function of Temperature (See FIGS. 2a and 2b ).

A single 3^(rd) order Polynomial curve is fitted to the data from −10°C. to +35° C., and from 165° C. to 200° C. using Microsoft ExcelTrendline tool (See FIGS. 2c and 2d ). The polynomial curve drawn isselected as the baseline for correction.

To obtain accurate heat of fusion (enthalpy) data, the polynomialbaseline is subtracted from the heat flow curve between −10° C. and 200°C. This is done by calculating the appropriate heat flow baseline valueat each data point and subtracting this value from the original heatflow value measured. This shifts the heat flow curve towards zero heatflux line (See FIG. 3a ). Once the baseline corrected heat flow data aregenerated, the plot is divided into three zones (See FIG. 3b ): Zone I(30-80° C.), Zone II (80-120° C.), and Zone III (120-170° C.).

The area under corrected heat flow curve is integrated with respect totime to determine the enthalpies in J/g for each of the threetemperature zones. The sum of the integrated enthalpy values from ZonesI and III, and the ratio of the integrated enthalpy value of Zone I tothe value for Zone III are calculated. Two specimens are run and theaverage integrated enthalpy for each zone is calculated. Average valuefor each zone is used to calculate and report average integratedenthalpy sum and average integrated enthalpy ratio.

Along with crystalline enthalpy, crystalline melting temperature of apolymer is measured using DSC method described above. Crystallinemelting point is defined as in the DSC method ASTM D3418-08, whichrefers to it as T_(pm).

3. Air Permeability Test

The air permeability of a substrate (e.g., film, laminate, or articlecomponent) is determined by measuring the flow rate of standardconditioned air through a test specimen driven by a specified pressuredrop. This test is particularly suited to materials having relativelyhigh permeability to gases, such as nonwovens, apertured films and thelike. ASTM D737 is used, modified as follows.

A TexTest FX 3300 instrument or equivalent is used, available fromTextest AG, Switzerland, or from Advanced Testing Instruments ATI inSpartanburg, S.C., USA. The procedures described in the OperatingInstructions for the TEXTEST FX 3300 Air Permeability Tester manual forthe Air Tightness Test and the Function and Calibration Check arefollowed. If a different instrument is used, similar provisions for airtightness and calibration are made according to the manufacturer'sinstructions.

The test pressure drop is set to 125 Pascal and the 5 cm² area test head(model FX 3300-5) or equivalent is used. The result is recorded to threesignificant digits. The average of 5 specimens is calculated andreported as the Air Permeability Value (m³/m²/min).

EXAMPLES

Polyolefin elastomers coded A to G, a styrenic block copolymer coded H,and elastomer compositions coded Examples 1-10 made by blending thepolyolefin elastomers A to G, were subjected to Tests 1-4 as follows,and reported in Table 1 below. The compositions of the polyolefinelastomers A to G are detailed below. All samples except Example H wereprovided as a film having a basis weight of 40 gsm.

Test 1: Average integrated enthalpy sum (J/gm) according to the ThermalAnalysis Method defined herein, DSC charts for Examples 1 to 8 shown asFIGS. 4(a) to 4(h).

Test 2: Average integrated enthalpy ratio according to the ThermalAnalysis Method defined herein.

Test 3: Unload stress at 75% strain above 0.8 MPa according to theHysteresis Test defined herein.

Test 4: Load stress/unload stress ratio at 75% strain of 1 to 2.6according to the Hysteresis Test defined herein.

A: Vistamaxx 6102 (available from ExxonMobil, Houston, Tex.): blend oftwo random propylene-ethylene copolymers exhibiting a single sharp glasstransition temperature (Tg) of about −32° C. and an overallcrystallinity of about 6 wt %. The crystalline phase exhibits twomelting peaks at about 50° C. and about 110° C.B: NOTIO PN-0040 (available from Mitsui Chemicals, Tokyo Japan): elasticpolyolefin resin with glass transition temperature of about −30° C.exhibiting two melting peaks at about 45° C. and about 157° C.C: L-MODU X901S (available from Mitsui Chemicals, Tokyo Japan): stereocopolymer of polypropylene with a Tg of about −5° C. and a crystallinityof about 13 wt %, exhibiting two melting peaks at about 50° C. and about68° C.D: Versify 2400A (available from Dow Chemical, Midland, Mich.): randomcopolymers of propylene with ethylene with glass transition temperatureof about −40° C. with crystalline phase having two melting peaks atabout 50° C. and about 140° C.E: Versify 2400B (available from Dow Chemical, Midland, Mich.): randomcopolymers of propylene with ethylene with glass transition temperatureof about −40° C. with crystalline phase having two melting peaks atabout 50° C. and about 140° C.F: Versify 3401A (available from Dow Chemical, Midland, Mich.): randomcopolymers of propylene with ethylene with glass transition temperatureof about −40° C., having a Crystalline phase with two melting peaks atabout 50° C. and about 95° C.G: Versify 3401B (available from Dow Chemical, Midland, Mich.): randomcopolymers of propylene with ethylene with glass transition temperatureof about −40° C. with crystalline phase having two melting peaks atabout 50° C. and about 140° C.H: Styrenic Copolymer blend made with hydrogenated Styrenic blockcopolymer, having a film basis weight (gsm) of 78.4. This material isknown to have favorable hysteresis performance, while being cost adding.

An Extruder manufactured by Berstorff (a division of KraussMaffeiCorporation, Florence, Ky.) under the name ZE25 is used to create samplefilms of Examples A-H and 1-10. This extruder has 25 millimeter screwdiameters, a length-to-diameter ratio of 32, and six heating/coolingbarrel zones along its length in addition to a cooled feeding zone. Adry blend of the polyolefin elastomers and any other materials, ifrequired, are tumbled to achieve a relatively uniform mixture, and thedry blend is fed to the extruder via a vibratory gravity feeder. Thefirst heating/cooling zone (barrel zone 2) is maintained at asufficiently high temperature to initiate softening of the polyolefinelastomers, and consists of conveying elements for transporting thematerials forward. The second through fourth heating/cooling zones(barrel zones 3-5) are each equipped with a high shearing forwardkneading element and forward conveying elements, while the fourthheating/cooling zone (barrel zone 5) is also equipped with a highshearing backward kneading element and the fifth heating/cooling zone(barrel zone 6) is equipped with a dispersion element and a reverseconveying seal element, all to facilitate increased pressure, shearing,and mixing of the low and high molecular weight components. The sixthand last heating/cooling zone (barrel zone 7) is equipped with forwardconveying elements intended to build sufficient pressure behind a castfilm die, and to facilitate extrusion through the die. For sample films1 through 10 in Table 1, the set temperature profile (barrel zones 2-7,transfer tube, die) is about 193° C., 204° C., 216° C., 232° C., 238°C., 249° C., with the screws being rotated at about 50 revolutions perminute. The extrusion die temperature after zone 7 is set at 249° C. Forsample film H, the set temperature profile (barrel zones 2-7, transfertube, die) is about 220° C., 230° C., 230° C., 230° C., 230° C., 230°C., 230° C., 230° C., with the screws being rotated at about 50revolutions per minute. A 25.4 cm wide coat hanger cast film die is usedto shape the material into a thin film, and a film take-off unit ispositioned to receive the extrudate which is collected on double sidedsilicone coated release paper and wound onto a cardboard roll. An airknife (Curtain Transvector® Air knife Model 921-12) at 275 kPa and atroom temperature was used in between the die and take-off roll to cooldown the material and to help with web handling/winding. The film basisweight is adjusted by varying the linear speed of the take-off unit. Forgenerating data herein, a mono-layer film of the material is collectedfrom the 254 mm cast film die, and the middle 127 mm is used. The filmis stored at room temperature (22±2° C.) and allowed to crystallize for3 to 6 weeks at room temperature to reach equilibrium.

Stress at break and % Strain at break of the sample films are measuredin cross machine direction using the Initial Tensile Test. They arereported in Table 2 below.

Pre-Straining and aging is conducted as follows: The extruded film ispre-strained in cross machine direction to simulate the activationprocess used in the production of elastic members useful for absorbentarticles. The film is pre-strained to 300% strain using tensile testerat 0.166 s⁻¹ strain rate and immediately returned to zero strain at0.166 s⁻¹. The ratio of initial gauge length to width of the sample isset to 1. The pre-strained film is then removed from the tensile testerand laid flat on a smooth surface. It is aged at 22±2° C. for 3-6 weeksto reach equilibrium. The film is analyzed by the Thermal AnalysisMethod and the Hysteresis Test as detailed above.

TABLE 1 Composition and Test 1 Test 3 Example weight percentage (J/gm)Test 2 (MPa) Test 4 A 100% A 8.97 >1000 1.0 1.94 B 100% B 24.45 3.490.87 3.78 C 100% C 31.39 >1000 0.86 6.94 D 100% D 11.00 8.85 0.77 2.08 E100% E 1.44 3.02 F 100% F 0.97 2.63 G 100% G 1.00 4.33 H 100% H 0.711.09 1 40% A, 36% E, 13.07 3.64 1.28 2.13 24% G 2 40% A, 60% E 15.352.19 1.29 2.30 3 40% A, 60% C 21.69 >1000 1.00 3.44 4 80% D, 20% E 14.523.11 1.03 2.15 5 40% A, 60% F 13.77 193.78 1.02 2.19 6 40% A, 60% D 9.6913.36 0.97 1.98 7 40% A, 60% B 15.28 4.89 1.03 2.56 8 60% E, 40% G 19.441.49 1.31 3.36 9 20% A, 48% E, 1.28 2.9 32% G 10  20% A, 80% C 0.78 5.0Examples 1-2 and 4-7 provided suitable hysteresis properties, and areexpected to provide good performance when used as stretch elements forabsorbent articles.

TABLE 2 Example Stress at Break (MPa) % Strain at Break (%) 1 24.4 798 221.4 740 4 13.0 750Examples 1, 2, and 4 provided suitable robustness to tensile stress, andare expected to provide good performance during processing for use asstretch elements for absorbent articles.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An elastomer composition comprising polyolefin elastomer material, said elastomer composition having the following properties: (1) an average integrated enthalpy sum of no greater than 17 J/g; (2) an average integrated enthalpy ratio of from 0.6 to 300; (3) an unload stress at 75% strain of above 0.8 MPa; and (4) a load stress/unload stress ratio at 75% strain of 1 to 2.6 according to the Hysteresis Test defined herein.
 2. An elastomer composition comprising polyolefin elastomer material, said elastomer composition having the following properties after having been pre-strained to 300% strain and aged for 3 weeks: (1) an average integrated enthalpy value of no greater than 17 J/g, according to DSC measurement, wherein the value of temperature zones between 30-80° C. and 120-170° C. are added; (2) an average integrated enthalpy ratio of from 0.6 to 300, when comparing the value of temperature zone between 30-80° C. to value of temperature zone between 120-170° C.; (3) an unload stress at 75% strain of above 0.8 MPa; and (4) a load stress/unload stress ratio at 75% strain of 1 to 2.6.
 3. The elastomer composition of claim 1 wherein the composition is prepared by extrusion blending at least 2 polyolefin elastomers.
 4. The elastomer composition of claim 3 wherein at least one of the at least 2 polyolefin elastomers has a crystalline melting point of at least 75° C.
 5. The elastomer composition of claim 3 wherein at least one of the at least 2 polyolefin elastomers comprises a metallocene polyolefin, preferably an elastomeric polypropylene.
 6. The elastomer composition of claim 1 having a crystalline melting point of at least 75° C.
 7. The elastomer composition of claim 1 having a stress at break of at least 10 MPa.
 8. The elastomer composition of claim 1 having a % Strain at break of at least 500%.
 9. The elastomer composition of claim 1, further comprising a bacteriostat.
 10. The elastomer composition of claim 1, further comprising a processing aid selected from the group consisting of synthetic and natural oils; hydrogenated synthetic and hydrogenated natural oils; naphthenic oils; paraffinic oils; olefin oligomers; vegetable oils; animal oils; petroleum derived waxes; and mixtures thereof.
 11. An elastic film made of the composition of claim 1 having a basis weight of from about 5 to about 150 g/m².
 12. The film of claim 11 wherein the film is breathable.
 13. A multi-layer laminate comprising the film of claim
 11. 14. The laminate of claim 13 wherein the laminate comprises one or more skin layers, said skin layer made of plastically extensible material.
 15. The laminate of claim 13 wherein the laminate comprises one or more skin layers, said skin layer made of elastic material.
 16. A component for an absorbent article made of the film or laminate of claim 11, said component selected from the group consisting of waistbands, leg elastic, side panels, elastic belts, stretch outer cover, and stretch ears.
 17. The elastomer composition of claim 2 wherein the composition is prepared by extrusion blending at least 2 polyolefin elastomers, wherein at least one of the at least 2 polyolefin elastomers has a crystalline melting point of at least 75° C., and wherein at least one of the at least 2 polyolefin elastomers comprises an elastomeric polypropylene.
 18. The elastomer composition of claim 2 having a crystalline melting point of at least 75° C.
 19. An elastic film made of the composition of claim 2 having a basis weight of from about 5 to about 150 g/m², wherein the film is breathable. 